How to Flush a Water Heater: Trust Us, What’s Inside Will Blow Your Mind

If the phrase “how to flush a water heater” has you wondering what the heck that is, you’re not alone. Although most homes have a water heater to warm up their showers, laundry, and other household tasks, many do not realize that this heater must be regularly flushed of debris. So how is this done?

“Flushing out the water heater drains sediment that collects in the bottom of the heater over time,” explains Don Glovan, a franchise consultant with Mr. Rooter Plumbing in Hendersonville, NC. “This maintenance step increases efficiency, prevents corrosion, and lengthens the appliance’s life.”

If you call up your local plumber to flush your water heater, you’re likely to be charged anywhere from $100 to $300. Not ready to part with all that cash? You’re in luck: This is a DIY task that most homeowners can manage, and a full flush needs to be done only once a year.

How to flush a water heater: Tools you’ll need

The main tools for this job are pliers, a small adjustable crescent wrench, and a garden hose—items most homeowners already have. It’s also helpful to have a transfer pump, which can be found at your local hardware or home improvement store.

Step 1: Turn off the utilities

Turn off the gas or oil that heats the water.

Ron Hazelton/YouTube

The first step in flushing a water heater is turning off the utilities that run to it, says Fred Webster, owner of MillTown Plumbing in Chelmsford, MA.

If you have a gas-powered water heater, you’ll need to turn the gas valve on your water heater to the off position. If you have one that’s electric, turn off the electricity. This may require turning it off right at the circuit breaker in your home.

Step 2: Shut off the cold water

The water supply typically has a knob like this.

Ron Hazelton/YouTube

Next, shut off the cold water that is leading into the heater. This valve is typically located near the top of your water heater.

Step 3: Turn on the hot water faucet

The hot water should run from a faucet throughout the process.

Ron Hazelton/YouTube

Turn on a hot water faucet in your home, ideally one nearest where your water heater is located. You’ll leave this on throughout the flushing process in order to prevent a vacuum from forming. When the heater is fully flushed, you’ll notice that water stops running out of the faucet, but leave it open!

Step 4: Give the water a place to go

A regular garden hose is part of the flushing process.

Ron Hazelton/YouTube

Connect a garden hose to the drain valve on your water heater, which is typically located on the side near the bottom. Run that hose to a drain, such as a sink. If you notice any leaking around the hose attachment, grab the pliers, and use them to tighten the hose to the valve.

You can also try a couple of buckets rather than a hose, but depending on the size of your tank, you could be facing 40 gallons of water or more that must be flushed out. You’ll need to make sure there’s somewhere for that water to go, and a bucket or two might not be enough.

If you don’t have a nearby drain to handle the flow of water, Webster says, you may need a transfer pump to help pump water to a suitable drainage location. Pumping the water outside is a popular option, but be sure to lay down a screen or catch the sediment that comes out along with the water.

Step 5: Open the drain valve

Sediment from the tank is natural, so don’t be freaked out when you see this gunk coming out.

Ron Hazelton/YouTube

Once your water has a place to go, open the drain valve, allowing the tank to completely drain. Be careful, the water may be hot! Also, don’t be alarmed by debris. This, after all, is why you’re flushing the heater in the first place.

Once the sediment stops coming out (typically in five to 10 minutes), this means your water heater is fully flushed out. At that point, you can close the drain valve, allowing the tank to refill.

You will want to leave your hot water faucet open during this entire process. The water will have stopped running out of the faucet when your heater was emptied—after all, there’s no water in the heater to come out—but once the tank has refilled, the water will again pump through your pipes, and feed the faucet. When water comes out of that faucet, you’ll know the tank is full.

A few words word of warning

Although this is a DIY-friendly project, Webster warns all homeowners to follow their manufacturer’s instructions when flushing a water heater. You should be able to find these near the temperature and pressure relief valve located on the side of the tank.

If you have an older system that has never been flushed, it may also be wise to call in a pro to handle the job, says Carlos Pineda, a professional plumber with ClipCall.

“If a water heater has never been flushed from date of installation and it has been three to five years, sometimes flushing the water heater will do more damage than good,” Pineda warns.

A pro can inspect your water heater to tell you if it’s good to flush. After that, the process should be done annually to keep your water heater in good shape.